Coaxial magnetron having magnetic return path through the cylindrical anode



COAXIAL MAGNETRON MAG TIC RETURN PATH THROU ODE A nl 2, 1968 w A. GERARD 3,376,466

HAVING GH THE CYLINDR L AN Filed Dec. 1, 1964 4o FIG.I.

N N i 24*: 5 \s WITNESSES INVENTOR M M William A Gerurd United States Patent cor oration of Pennsylvania p Filed Dec. 1, 1964, Ser. No. 415,074

2 (ilaims. (Cl. SIS-39.71)

ABSTRACT OF THE DISCLOSURE The present invention relates to a coaxial magnetron in which the magnetic circuitry provides that magnets are positioned substantially coaxially with respect to the cathode of the magnetron and the magnetic field return is provided by means of the anode of the magnetron.

This invention relates to magnetrons and more particularly, to coaxial cavity magnetrons.

In R. J. Collier et al. US. Patent 2,854,603 issued Sept. 30, 1958 there is described a coaxial magnetron structure which comprises an inner and outer resonant system. The inner resonant system includes a cylindrical anode to gether with a plurality of anode vanes radially extending inwardly therefrom. These vanes define a circumferential array of inner, or anode cavity resonators. An outer cavity resonator is defined between an outer cylindrical wall and the cylindrical anode. The two systems are coupled together by a circumferential array of uniformly spaced slots through the cylindrical anode which connect the outer resonant system with alternate ones of the anode cavity resonators. The inner resonant system is des gned to oscillate in a pimode, while the other system 15 designed to oscillate in the TE mode.

Such structural arrangements overcome many d sadvantages inherent in magnetrons of the prior conventional design. More particularly, the coaxial magnetron arrangement permits the realization of substantially high frequency stability and efiiciency simultaneously under varying input and load conditions. The turnng function of the coaxial magnetron is provided within the outer cavity resonator in a manner such as described in US. Patent 3,263,118, by H. P. Peasley et al., filed July 30, 1963 and assigned to the same assignee as this invention. These conventional coaxial magnetrons are somewhat larger than the prior art type of magnetron and are of increased weight. This is often due to the large size of the coaxial T mode cavity and the need for the magnet to enclose it.

It is accordingly an object of this invention to provide an improved coaxial magnetron.

It is another object to provide an improved coaxial magnetron in which the tuning mechanism is external of the vacuum envelope.

It is another object to provide an improved coaxial magnetron in which the outer cavity resonator and the associated tuning mechanism are exterior of the vacuum envelope so that on failure of the magnetron it is not necessary to replace the tuning assembly and the outer cavity resonator.

It is another object to reduce the magnetic circuitry bulk associated with a conventional coaxial magnetron.

Briefly, the present invention provides a coaxial magnetron in which an evacuated electromagnetic t ransmissive envelope surrounds the inner structure of the magnetron so that the anode cylinder and the inner resonant system is combined within the envelope and the outer cavity resonator is positioned exterior of the envelope to mechanically isolate the outer cavity resonator lfl'Ol'Il. the inner structure and yet provide electrical coupling between the inner resonant system and the outer resonant cavity. Another feature of the invention is that the magnetic circuitry provides that the magnets are positioned substantially coaxially with respect to the cathode of the magnetron and the magnetic field return is provided by means of the coaxial magnetron anode.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of the specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a sectional view of a coaxial cavity magnetron embodying the present invention; and

FIG. 2 is a View taken along the line II-II of FIG. 1.

Referring now to the drawing, the specific embodiment of the invention is shown in FIGS. 1 and 2 and comprises a magnetron 10 having a cylindrical cathode 11 surrounded by a cylindrical anode 12. Extending inwardly from the anode 12 are a plurality of anode vanes 14 which define therebetween a plurality of anode resonators 16. A plurality of slots 18 extend through the anode 12 along a major portion of its length and parallel to the vanes 14. In the specific embodiment shown, the slots 18 communicate with alternate ones of the anode resonators 16.

Positioned at one end of the anode 12 is a magnetic pole piece 20 which is annular in shape. The cathode 11 extends into the aperture provided in the pole piece 20. The pole piece 20 may be of a suitable material such as iron. In physical and magnetic contact with the pole piece 20 is an annular magnet 22. The polarity of the magnet is indicated in the drawing with the north pole adjacent the pole piece 20. Positioned at the opposite end of the anode 12 with respect to the pole piece 20 is annular pole piece 24 which again is of suitable magnetic material and in physical contact with a magnet 26 in which the south pole is adjacent the pole piece 24.

The cylindrical anode 12 is closed off by end plates 30 and 32 which are secured to the magnets 26 and 22 respectively and to the anode 12. The end caps 30 and 32 as well as the anode 12 must be of or include magnetic material such as iron to provide the return path for the magnetic field from the magnets 22 and 26. The anode 12 must be provided with electrically conductive material on both the inner and outer surface. This requires that a suitable conductive coating of a material such as copper be provided on the body if it is of a suitable magnetic material such as iron.

Encompassing the cylindrical anode 12 is a ceramic cylindrical envelope member 40 transmissive to the electromagnetic energy generated within the anode cylinder 12. The ceramic envelope 40 may be closed off at the ends by dome members 44 and 46 to provide a vacuum envelope. Suitable leads may extend through one of the dome-like members 44 or 46 to provide suitable voltages to the electrodes. Alternately, the ceramic cylinder 40 may be terminated in metal to ceramic seals which may be attached to end plates 30 and 32.

An outer cavity resonator 49 surrounds the envelope 40. The cavity resonator 49 is defined by a cylindrical member 50, end plates 52 and 54 and the anode 12. The unitary walls 50, 52 and 54 which surround the inner electron tube structure and the anode :12 is readily removable therefrom. This cavity resonator 49 is designed to operate in the TE mode.

The end plate 54 is annular in shape and may be designed to be movable in an axial direction to modify or change the dimensions of the cavity resonator 49 to provide tuning thereof. Suitable tuning means is described in the above mentioned copending application. The outer resonator cavity 49 is exterior of the evacuated portion of the magnetron. This greatly reduces the cost of the output cavity 49'. The cavity 49 has little or no pressure difference across its walls and reinforcement of the walls is not needed. The weight of the complete magnetron package is thus reduced since the walls 50, 52 and 54 may be made from aluminum with suitable electrically conducting coatings of materials such as copper or silver. This change of material is also possible in view of the fact that vacuum processing of the cavity resonator 49 is unnecessary. The tuning mechanism may be very simple and does not require complicated vacuum joints. Failure of the magnetron cathode does not require changing the cavity tuner.

In the operation of the device, the cathode, is periodically biased at a negative potential with respect to the rest of the device by means of a suitable source of potential (not shown). Electrons are then emitted from the cathode 11 and are constrained to flow in a circular path between the cathode 11 and the anode 12 by the cross field focusing action of the electric field between the cathode 11 and the anode 12 and the magnetic field between the pole pieces and 24. The beam excites electric fields in the anode resonators 16. The magnetron oscillates in the pi-mode at a characteristic frequency determined by the anode resonators 16. This energy is then coupled to the outer cavity resonator 49 by means of the coupling slots 18. The electric field produced in the resonator 49 oscillates in a TE mode at a frequency determined by the position of the movable end wall 54. The output resonator 49 is connected by suitable transformer means to an output wave guide section to which the output energy of the magnetron is transmitted to external circuitry.

While there have been shown and described what are presently considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. For example, while the design illustrated provides for the magnets to be included within the vacuum enclosure, it is obvious that the magnets may be provided external to the vacuum and yet still utilize the anode cylindrical wall as the return path for the magnet. It is also possible to provide ceramic windows in the slots 18; In this manner the anode 12 may form the evacuated envelope with the ceramic domes 44 and 46 sealed to the anode 12 and the cylindrical member 40 may be dispensed with.

It is not desired, therefore, that the invention be limited 4 to the specific arrangement shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. A coaxial magnetron comprising an axial cathode, a cylindrical anode coaxialwith said cathode and surrounding said cathode, an array of anode vanes extending radially inwardly from said cylindrical anode wall and defining a plurality of anode resonators, magnets positioned at opposite ends of the region defined between said cathode and said anode for providing a magnetic field parallel to the axis of said tube, said magnets including pole pieces projecting into said region, end caps of magnetic material contacting said magnets and said cylindrical anode to provide a magnetic path between said magnets, said anode resonators provided with slots in alternate resonators and a coaxial cavity resonator surrounding said cylindrical anode for receiving the energy generated within said region and coupled thereto through said slots in saidcylindrical wall.

2. A magnetron comprising a cylindrical cathode, a cylindrical anode surrounding said cathode and coaxial therewith, an array of anode vanes extending radially inward from said anode wall and defining a plurality of anode resonators, means'for producing a magnetic field in a direction substantially transverse to the direction of motion of electrons emitted from said cathode and directed toward said anode, said means comprising a magnet positioned at one end of the space defined by said 'anode resonator and a second magnet positioned at the opposite end of said anode resonator space and magnetic circuit means connecting said magnets comprising said cylindrical anode and end cap members and an output cav-ity resonator surrounding said cylindrical anode and said cylindrical anode having slots therein for coupling energy from said anode resonators to said output resonator.

References Cited UNITED STATES PATENTS 2,452,272 10/1948 Tiley 3'1539.77 2,523,286 9/1950 Fiske et a1,

2,565,387 8/1951 McCarthy 3l539.65 X 3,263,118 7/1966 Peasley et a1. 315-39151 X ELI LIEBERMAN, Primary Examiner. HERMAN K. SAALBACH, Examiner. P. L. GENSLER, Assistant Examiner. 

